The invention relates generally to the field of heating, ventilating, air conditioning, and refrigeration (HVAC&R) systems, and more particularly to heat pump systems with a flow directing system that allows a heat exchanger to be switchable between a single-pass arrangement and a two-pass arrangement.
A wide range of applications exist for heating, ventilating, air conditioning and refrigeration (HVAC&R) systems. For example, residential, light commercial, commercial and industrial systems are used to control temperatures and air quality in residences and buildings. Very generally, these systems operate by implementing a thermal cycle in which fluids are heated and cooled to provide the desired temperature in a controlled space, typically the inside of a residence or building. Similar systems are used for vehicle cooling, and as well as for general refrigeration.
Controlled fluids within such systems are typically confined with enclosed circuits and include various refrigerants. Refrigerants are specifically formulated to undergo phase changes within the normal operating temperatures and pressures of the systems so that considerable quantities of heat can be exchanged by virtue of the latent heat of vaporization of the circulated refrigerant. In most such systems, for example, the refrigerant is evaporated in one heat exchanger to draw heat from air circulating through the heat exchanger for cooling purposes. Conversely, the refrigerant is then condensed in a different heat exchanger to release heat from the refrigerant and thereby heat an air stream. Depending upon whether the evaporating heat exchanger and condensing heat exchanger are inside of the controlled space or outside of the controlled space, the system will function to heat or cool the air within the space.
In heat pump systems, the direction of refrigerant flow through evaporating and condensing heat exchangers can be reversed to allow for extraction of heat from a controlled space (cooling mode) and for the injection of heat into the space (heating mode). For example, in the cooling mode, vapor phase refrigerant may flow in a first direction from a compressor to an outdoor heat exchanger that condenses the refrigerant. The liquid refrigerant may then flow through an expansion device to an indoor heat exchanger that evaporates the refrigerant to cool the controlled space. Accordingly, in the cooling mode, the outdoor heat exchanger operates as a condenser and the indoor heat exchanger operates as an evaporator. In the heating mode, refrigerant flows through the system in an opposite direction, and the roles of the heat exchangers are reversed. For example, vapor phase refrigerant may flow from the compressor to the indoor heat exchanger, which condenses the refrigerant to heat the controlled space. The refrigerant may then flow through the expansion valve to the outdoor heat exchanger, which evaporates the refrigerant. The refrigerant then flows to the compressor to repeat the cycle through the system. Accordingly, in the heating mode, the outdoor heat exchanger operates as an evaporator and the indoor heat exchanger operates as a condenser.
In typical heat pump systems, the direction of flow within the system is reversed to switch the heat pump system between a cooling mode and a heating mode. Accordingly, the flow of refrigerant through the heat exchangers is reversed, and consequently, the refrigerant flows through a heat exchanger with the same number of passes in both the heating and cooling modes. However, it may be inefficient and/or undesirable to employ the same number of passes for both the heating and cooling modes of operation.